Electrical switch



y 1939- E. T. ABENDROTH ELECTRICAL SWITCH Filed July 8, 1938 1 l J 4 a iii .5

RM Y /N 4v WW 0 NM T I A 0 n 2 r 2 Kg 3 f 0 f 3 W & l B W a m Patented May 9, 1939- PATENT OFFICE ELECTRICAL SWITCH Elmer T. Abendroth, Tipton, Ind., assignor to The Oakes Manufacturing Company, Tipton, End, a

corporation Application July 8, 1938, Serial No. 218,071

4 Claims.

This invention relates to an electrical switch and more particularly to that type of snap switch known as a micro switch. Such switches are generally used in thermostatic operation and in other cases requiring positive opening and closing of a switch with a very small actuating force operating through an extremely short distance.

One object of the present invention is to provide a micro switch of extremely rugged and durable construction. To this end there is provided a switch in which a single spring performs the functions of holding the switch in its normal position, returning the same thereto and snapping the contact points to and from their open and closed. positions. All other moving parts of the switch are of rigid construction as distinguished from resilient spring members and thus are much more durable and better adapted to the purpose intended.

Another object of the invention is to provide a switch in which the force tending to return the same to normal position decreases rather than increases during the movement thereof from the normal position. This result is obtained by an arrangement of parts described in detail in the following specification and makes certain that the switch when once started from the normal position by any suitable actuating force is positively and instantaneously operated.

Other objects and features of the invention will be understood from the accompanying drawing and the following description and claims.

Fig. l is an elevational view with parts cut away of a switch having the invention embodied therein in one of its preferred forms. Said views shows the switch in its normal position. Fig. 2 is a similar view with the switch in its actuated position. Figs. 3 and 4 are perspective views of two of the moving parts of the switch removed therefrom. Fig. 5 is a perspective view of stationary parts of the switch with the moving parts removed therefrom. Figs. 6 and '7 are diagrammatic views illustrating the intersection of the forces within the switch in the normal and actuated positions respectively.

In the preferred form of the invention illustrated in the drawing, the base of the switch consists of an insulation block it having in the bottomthereof a groove ii in which there are positioned apair of terminal bars l2 and i3. Said bars may be provided with terminal screws M for the connection of conductors in the usual manner. Adjacent one end of the block it there is inset therein a threaded bushing I5 which receives a screw it securing the terminal bar l2 thereto. The upper end of the bushing it receives a screw ll which serves to secure in place an L-shaped member 88. The member i8 is provided on its inner face with a knife edge seat H! in which there is seated one edge of a rigid member 20 shown in detail in Fig. 4. Said member is generally channel-shaped to provide strength and stiffness and one end thereof is provided with Wings 2! embracing the member l8 and serving to retain the same in proper relation thereto. The opposite end of the member 20 carries a contact point 22 adapted to engage a stationary contact point 23 carried on the block H1 and connected to the contact bar i3 by a screw 26. When the contact points 22 and 23 are in engagement an electrical connection is complete from the terminal i2 to the terminal 53 through screw it, bushing 85, screw ll, member 88, member 26, contact points 22 and 23 and screw 2 The operation of said points breakfl said connection.

The member 58 is also provided with a knifi edge seat 25 positioned in the outer face thereoi and above the seat it. The seat 25 is engaged by a knife edge 26 formed on a stirrup 2i embracing the member 58 and rigidly secured to a member 28 shown in detail in Fig. 3. The member 28 and the stirrup 27 together form a rigid structure. The member 28 has a downwardly curved portion 29 passing about the end of the shorter member 25 and having formed therein a knife edge seat The member Zii has a portion 38 thereof upwardly bent to form a similar knife edge seat at 32. An arched leaf spring 33 is interposed between the members Zll and 28 and has its ends forming knife edges resting in the seats 30 and 32. Said spring, therefore, exerts opposing forces on the members iii and 2B in the direction of a line drawn through the seats 30 and 32. These forces serve to hold said members against their knife edge seats i9 and 25.

An L-shaped stop member 36 is secured to the base it] by means of a screw 35 and is provided with a cross bar 36 limiting the upward movement of the member 28 about its knife edge pivot 25. The stop member 3% is also provided with a cross bar 31 limiting the upward movement of the member 20 about its knife edge pivot l9. The

I downward movement of the member 28 is limited by engagement of the curved end 29 thereof with the block It), while the downward movement of the members 20 is limited by engagement of the contact points 22 and 23. -A cover 38 is secured to the block it] and carries a bushing 39 in which there is mounted a push button iii 40 engaging the upper surface of the member 28 and projecting outside of the cover 38.

In Figs. 6 and 7, the relative positions of the moving parts and the several knife edge seats are diagrammatically shown. The spring 33 exerts opposing forces on the seats 30 and 32, the directions of said forces being indicated by arrows I and 42, both of which lie in the prolongations of a line joining said seats. In the normal position of the switch shown in Fig. 6, this line passes below the seats l9 and 25. The force indicated by the arrow 42 therefore exerts a counterclockwise moment on the member 20 which serves to hold the contact point 22 against the contact point 23. The force indicated by the arrow 4| on the other hand, exerts a clockwise moment on the member 28, tending to hold the same against its stop 36. When an external force is applied to the push button 40 as indicated by the arrow 43 in Fig. 7, the member 28 is moved downwardly about its pivot point 25 and the relative positions of the seats 30 and 32 are changed. In this movement of the member 28 the line of direction of the forces crosses the pivot l9 and approaches but does not quite reach the pivot 25, as shown by the arrow 42 in Fig. 7. Thus, the moment exerted by the spring 33 on the member 20 is changed in direction and said member is moved upwardly with a snap action and held against its stop 31. The moment exerted by the spring on the member 28, however, is still in the same direction but is greatly decreased since its lever arm, represented by the perpendicular distance between the pivot point 25 and the arrow 42, has greatly diminished. This moment however is always suflicient to return the switch to its normal position when the pressure on the push button has been removed.

From the foregoing analysis of the forces involved, it will be apparent that the pressure re quired on the push button 40 to move the member 28 against the action of spring 33 decreases as said member is moved from its normal position. Thus, any force strong enough to start the operation of the switch is more than strong-enough to finish it. The switch is thus instantly responsive to a small change of pressure on the push button and has the sensitive characteristic required of a good micro switch. Furthermore, the only resilient member in the switch is the spring 33 which supplies all of the necessary forces for the operation of the switch except the external actuating force. Other moving parts are of rigid construction not subjected to bending fatigue. The provision of knife edge bearings at the four fulcrum points reduces friction to a minimum.

The foregoing specification describes the invention in one of its preferred forms the details of whichmay be varied by those skilled in the art without departing from the scope of the invention as defined by the appended claims. For example. the switch herein shown is of the normally closed type. The changes required to adapt the invention to a normally open switch or to a switch having both normally open and normally closed contact elements will be obvious. Preferably, the switch is constructed on a much smaller scale than is shown in the drawing, but the principles thereof are not limited to a switch of any particular size.

The invention claimed is:

1. In a snap switch, a pair of rigid members of unequal length pivotally mounted at adjacent points and extending generally in the same directionfrom their pivot points, the longer of said members having the end thereof remote from its pivot point curved about and spaced from the corresponding end of the shorter of said members, a compression spring interposed between the curved portion of the longer member and a portion of the shorter member and exerting opposing forces thereon directed along a line passing through the region of said pivot points, a contact point carried by the shorter member, a mating stationary contact point, and stops limiting the pivotal movement of the longer member in both directions and limiting the movement of the shortermember away from said mating contact point, the points of application of the force of said spring being so located that the line of force thereof remains on one side of the pivot of the longer member irrespective of the position of said member between its stops but passes over the pivot point of the shorter member when the longer member is moved from one of its stops to the other, whereby said spring constantly urges the longer member in one direction but alternately urges the shorter member toward and away from the mating contact point as the longer member is moved.

2. In a snap switch, a pair of rigid members of unequal length pivotally mounted at adjacent points and extending generally in the same direction from their pivot points, the longer of said members having the end thereof remote from its pivot point curved about and spaced from the corresponding end of the shorter of said members, a compression spring interposed between the curved portion of the longer member and a portion of the shorter member and exerting opposing forces thereon directed along a line passing through the region of said pivot points, a contact point carried by the shorter member, a mating stationary contact point, and stops limiting the pivotal movement of the longer member in both directions and limiting the movement of the shorter member away from said mating contact point, the points of application of the force of said spring being so located that the line of force thereof in the normal position of said switch passes on the same side of both pivot points and as said longer member is moved from its normal position said line of force crosses the pivot point of the shorter member and approaches but does not reach the pivot point of the longer member, whereby the turning movement of said spring on the shorter member is reversed in direction and the turning movement thereof on the longer member is decreased but not reversed as the longer member is moved from its normal position.

3. In a snap switch, a pair of rigid members of unequal length pivotally mounted at adjacent points and extending generally in the same direction from their pivot points, the longer of said members having the end thereof remote from its pivot point curved about and spaced from the corresponding end of the shorter of said members, the longer of said members having a knife edge seat formed in the curved portion thereof and the shorter of said members having a knife edge seat formed thereon, an arched leaf spring having its ends seated in said seats and exerting opposing forces thereon, a contact point carried by the shorter member, a mating stationary contact point, and stops limiting the pivotal movement of the longer member in both directions and limiting the movement of the shorter member away from said mating contact point, the position of said seats being such that a line joining the same and prolonged to the region of the pivot points remains on one side of the pivot of the longer member irrespective of the position of said member between its stops but passes over the pivot oi! seat formed in the curved portion thereof and: the shorter of said members having a knife edge seat formed thereon, an arched leaf spring having its end seated in said seats and exerting opposing forces thereo a contact point carried by the shorter member, a mating stationary contact point, and stops limiting the pivotal movement of the longer member in both directions and limiting the movement of the shorter member away from said mating contact point, the position 01' said seats being such that a line joining the same and prolonged to the region of the pivot points passes on the same side of both pivot points when said switch is in its normal position but crosses over the pivot point of the shorter member and approaches but does not reach that of the longer member when the latter is moved from its normal position.

EIMER T. ABENDROTH. 

